diff --git a/frontend/web/src/App.tsx b/frontend/web/src/App.tsx
index 2013642..fbedf70 100644
--- a/frontend/web/src/App.tsx
+++ b/frontend/web/src/App.tsx
@@ -1,6 +1,6 @@
 import { useEffect, useState } from "react";
 import { TopBar } from "./components/TopBar";
-import { Sidebar, BottomNav } from "./components/Nav";
+import { Sidebar } from "./components/Nav";
 import { ModeRouter } from "./modes/ModeRouter";
 import { AdminApp } from "./admin/AdminApp";
 import { parseAdminHash } from "./admin/router";
@@ -34,11 +34,10 @@ export default function App(): React.ReactNode {
       <TopBar />
       <div className="flex min-h-0 flex-1">
         <Sidebar />
-        <main className="relative flex-1 overflow-y-auto pb-[var(--mu-bottomnav-h)] md:pb-0">
+        <main className="relative min-h-0 flex-1 overflow-y-auto">
           <ModeRouter />
         </main>
       </div>
-      <BottomNav />
     </div>
   );
 }
diff --git a/frontend/web/src/components/ChatInput.tsx b/frontend/web/src/components/ChatInput.tsx
index b395af9..62ebefe 100644
--- a/frontend/web/src/components/ChatInput.tsx
+++ b/frontend/web/src/components/ChatInput.tsx
@@ -1,25 +1,14 @@
 import { useEffect, useRef, useState } from "react";
 import { Button } from "./primitives";
-import { Icon, type IconName } from "./Icon";
-import { useModeStore } from "../store/useModeStore";
-import type { Mode } from "../lib/types";
+import { Icon } from "./Icon";
 
 export interface ChatInputProps {
-  onSend: (text: string, mode: Mode) => void;
+  onSend: (text: string) => void;
   sending: boolean;
   onVoice: () => void;
   placeholder?: string;
 }
 
-const INPUT_MODES: ReadonlyArray<{ mode: Mode; label: string; icon: IconName }> = [
-  { mode: "chat", label: "对话", icon: "chat" },
-  { mode: "code", label: "代码", icon: "terminal" },
-  { mode: "home", label: "家居", icon: "home" },
-  { mode: "work", label: "工作", icon: "folder" },
-  { mode: "docs", label: "知识库", icon: "docs" },
-  { mode: "vision", label: "视觉", icon: "vision" },
-];
-
 export function ChatInput({
   onSend,
   sending,
@@ -28,8 +17,6 @@ export function ChatInput({
 }: ChatInputProps): React.ReactNode {
   const [value, setValue] = useState("");
   const taRef = useRef<HTMLTextAreaElement>(null);
-  const mode = useModeStore((s) => s.mode);
-  const setMode = useModeStore((s) => s.setMode);
 
   // auto-grow the textarea up to a max height
   useEffect(() => {
@@ -42,31 +29,12 @@ export function ChatInput({
   const submit = () => {
     const t = value.trim();
     if (!t || sending) return;
-    onSend(t, mode);
+    onSend(t);
     setValue("");
   };
 
   return (
     <div className="glass sticky bottom-0 border-t border-[var(--mu-glass-border)] p-3 md:p-4">
-      {/* input-mode switcher: sets the mode for the NEXT message (design/07 §1). */}
-      <div className="mx-auto mb-2 flex max-w-2xl items-center gap-1 overflow-x-auto pb-0.5">
-        <span className="mr-1 shrink-0 text-[10px] text-[var(--mu-text-lo)]">行为模式</span>
-        {INPUT_MODES.map(({ mode: m, label, icon }) => (
-          <button
-            key={m}
-            onClick={() => setMode(m)}
-            className={`inline-flex shrink-0 items-center gap-1 rounded-[var(--mu-radius-pill)] px-2.5 py-1 text-xs transition-all duration-200 ease-[var(--mu-spring)] active:scale-95 ${
-              mode === m
-                ? "bg-[var(--mu-accent)]/15 text-[var(--mu-accent-hi)]"
-                : "bg-[var(--mu-surface-4)] text-[var(--mu-text-mid)] hover:bg-[var(--mu-surface-5)]"
-            }`}
-          >
-            <Icon name={icon} size={13} />
-            {label}
-          </button>
-        ))}
-      </div>
-
       <div className="mx-auto flex max-w-2xl items-end gap-2 rounded-[var(--mu-radius-lg)] bg-[var(--mu-surface-2)] p-2 shadow-[var(--mu-shadow-1)]">
         <textarea
           ref={taRef}
diff --git a/frontend/web/src/components/Nav.tsx b/frontend/web/src/components/Nav.tsx
index f60f4fa..cb2f268 100644
--- a/frontend/web/src/components/Nav.tsx
+++ b/frontend/web/src/components/Nav.tsx
@@ -1,87 +1,100 @@
-import { useModeStore } from "../store/useModeStore";
-import { sendUp } from "../lib/ws";
-import { MODES, type Mode } from "../lib/types";
+import { useState } from "react";
+import { applyTheme, readTheme, type ThemeMode } from "../lib/theme";
+import { getAuthToken } from "../lib/api";
+import { useAppStore } from "../store/useAppStore";
 import { Icon, type IconName } from "./Icon";
+import { Tag } from "./primitives";
 
-const NAV_MODES: ReadonlyArray<Mode> = [
-  "chat", "code", "home", "work", "docs", "voice", "vision", "agents",
-];
-
-const modeMeta: Record<Mode, { label: string; icon: IconName }> = {
-  chat: { label: "对话", icon: "chat" },
-  code: { label: "代码", icon: "terminal" },
-  home: { label: "家居", icon: "home" },
-  work: { label: "工作", icon: "folder" },
-  docs: { label: "知识库", icon: "docs" },
-  voice: { label: "语音", icon: "mic" },
-  vision: { label: "视觉", icon: "vision" },
-  agents: { label: "子代理", icon: "agent" },
-  settings: { label: "设置", icon: "settings" },
-};
-
-/** Sets the input mode — the mode of the NEXT message (design/07 §1). In the
- *  single-page design this no longer switches pages; it only shapes the next
- *  bubble and notifies the backend for a mode-aware reply. */
-function useSwitchMode(): (m: Mode) => void {
-  const setMode = useModeStore((s) => s.setMode);
-  return (m: Mode) => {
-    setMode(m);
-    sendUp({ type: "mode_switch", data: { mode: m } });
-  };
-}
-
+/**
+ * Left rail — NOT a behavior-mode list (design/01 §3: mode switching is driven
+ * at runtime by the agent / user, and rendered per message). This is a small
+ * navigation rail: brand + connection status + theme + admin/settings entry.
+ */
 export function Sidebar(): React.ReactNode {
-  const mode = useModeStore((s) => s.mode);
-  const switchMode = useSwitchMode();
+  const wsStatus = useAppStore((s) => s.wsStatus);
+  const mood = useAppStore((s) => s.mood);
+  const [theme, setTheme] = useState<ThemeMode>(readTheme);
+  const connected = wsStatus === "connected";
+  const hasToken = !!getAuthToken();
+
+  const toggleTheme = () => {
+    const next: ThemeMode = theme === "dark" ? "light" : "dark";
+    applyTheme(next);
+    setTheme(next);
+  };
 
   return (
     <nav className="glass hidden h-full w-[var(--mu-sidebar-w)] shrink-0 flex-col gap-1 border-r border-[var(--mu-glass-border)] p-3 md:flex">
-      <div className="px-2 py-2 text-xs font-semibold uppercase tracking-wider text-[var(--mu-text-lo)]">
-        行为模式
+      <div className="flex items-center gap-2 px-2 py-2">
+        <img src="/icon.svg" alt="Cyrene" className="h-7 w-7" />
+        <div className="leading-tight">
+          <div className="text-sm font-semibold">Cyrene</div>
+          <div className="text-[11px] text-[var(--mu-text-lo)]">昔涟</div>
+        </div>
+      </div>
+
+      {/* connection status */}
+      <NavItem
+        active={connected}
+        icon="channel"
+        label={connected ? "实时连接" : "未连接"}
+        onClick={() => {}}
+        hint={wsStatus}
+      />
+
+      {mood ? (
+        <div className="px-2 py-1 text-[11px] text-[var(--mu-text-lo)]">
+          心情 · {mood}
+        </div>
+      ) : null}
+
+      <div className="mt-auto flex flex-col gap-1">
+        <NavItem
+          icon="settings"
+          label="设置"
+          onClick={() => { window.location.hash = "#/admin/system"; }}
+        />
+        <NavItem
+          icon="shield"
+          label="管理面板"
+          onClick={() => { window.location.hash = "#/admin"; }}
+        />
+        <NavItem
+          icon={theme === "dark" ? "sun" : "moon"}
+          label={theme === "dark" ? "浅色" : "深色"}
+          onClick={toggleTheme}
+        />
+        {!hasToken ? <Tag tone="warn">未登录</Tag> : null}
       </div>
-      {NAV_MODES.map((m) => {
-        const meta = modeMeta[m];
-        const active = m === mode;
-        return (
-          <button
-            key={m}
-            onClick={() => switchMode(m)}
-            className={`flex items-center gap-2.5 rounded-[var(--mu-radius)] px-3 py-2 text-sm transition-all duration-200 ease-[var(--mu-spring)] active:scale-[0.98] ${
-              active
-                ? "bg-[var(--mu-accent)]/15 font-medium text-[var(--mu-accent-hi)]"
-                : "text-[var(--mu-text-mid)] hover:bg-[var(--mu-surface-4)]"
-            }`}
-          >
-            <Icon name={meta.icon} size={18} />
-            <span>{meta.label}</span>
-          </button>
-        );
-      })}
     </nav>
   );
 }
 
-export function BottomNav(): React.ReactNode {
-  const mode = useModeStore((s) => s.mode);
-  const switchMode = useSwitchMode();
+function NavItem({
+  icon,
+  label,
+  onClick,
+  active = false,
+  hint,
+}: {
+  icon: IconName;
+  label: string;
+  onClick: () => void;
+  active?: boolean;
+  hint?: string;
+}): React.ReactNode {
   return (
-    <nav className="glass fixed inset-x-0 bottom-0 z-30 flex h-[var(--mu-bottomnav-h)] items-stretch border-t border-[var(--mu-glass-border)] md:hidden">
-      {NAV_MODES.slice(0, 5).map((m) => {
-        const meta = modeMeta[m];
-        const active = m === mode;
-        return (
-          <button
-            key={m}
-            onClick={() => switchMode(m)}
-            className={`flex flex-1 flex-col items-center justify-center gap-0.5 text-[11px] transition-colors duration-200 ${
-              active ? "text-[var(--mu-accent-hi)]" : "text-[var(--mu-text-lo)]"
-            }`}
-          >
-            <Icon name={meta.icon} size={18} />
-            <span>{meta.label}</span>
-          </button>
-        );
-      })}
-    </nav>
+    <button
+      onClick={onClick}
+      className={`flex items-center gap-2.5 rounded-[var(--mu-radius)] px-3 py-2 text-sm transition-all duration-200 ease-[var(--mu-spring)] active:scale-[0.98] ${
+        active
+          ? "bg-[var(--mu-accent)]/15 font-medium text-[var(--mu-accent-hi)]"
+          : "text-[var(--mu-text-mid)] hover:bg-[var(--mu-surface-4)]"
+      }`}
+    >
+      <Icon name={icon} size={18} />
+      <span>{label}</span>
+      {hint ? <span className="ml-auto text-[10px] text-[var(--mu-text-lo)]">{hint}</span> : null}
+    </button>
   );
 }
diff --git a/frontend/web/src/lib/api.ts b/frontend/web/src/lib/api.ts
index 422b10d..3f5c289 100644
--- a/frontend/web/src/lib/api.ts
+++ b/frontend/web/src/lib/api.ts
@@ -155,10 +155,10 @@ export function chatSync(
 }
 
 /** POST /api/v1/chat with stream:true — triggers streaming over the WS channel. */
-export function chatStream(sessionId: string, text: string, mode?: Mode): Promise<{ stream: true }> {
+export function chatStream(sessionId: string, text: string): Promise<{ stream: true }> {
   return request<{ stream: true }>("/chat", {
     method: "POST",
-    body: JSON.stringify({ sessionId, text, stream: true, mode }),
+    body: JSON.stringify({ sessionId, text, stream: true }),
   });
 }
 
diff --git a/frontend/web/src/lib/useChat.ts b/frontend/web/src/lib/useChat.ts
index 9a8c453..2440773 100644
--- a/frontend/web/src/lib/useChat.ts
+++ b/frontend/web/src/lib/useChat.ts
@@ -2,19 +2,18 @@ import { useCallback, useState } from "react";
 import { chatStream } from "./api";
 import { connectWs, isWsOpen } from "./ws";
 import { useAppStore } from "../store/useAppStore";
-import { useModeStore } from "../store/useModeStore";
 import { now } from "./util";
-import type { Mode } from "./types";
 
 /** Drives one user turn: push the user bubble, blanket a streaming assistant
  *  bubble, trigger the backend loop over REST (`stream:true`), and let the WS
  *  stream render into that bubble. Falls back to the WS `chat` channel when the
  *  REST trigger fails so the demo still works without a wired loop.
  *
- *  Each message carries the current input mode, so its bubble renders per that
- *  mode (design/07 §1: shared message stream, per-message mode rendering). */
+ *  The behavior mode is NOT chosen by the user at send time — the agent / backend
+ *  hot-switches it (design/01 §3), and each message carries its own mode, so the
+ *  bubble renders per that message's mode. */
 export function useSendChat(): {
-  send: (text: string, mode?: Mode) => Promise<void>;
+  send: (text: string) => Promise<void>;
   sending: boolean;
 } {
   const [sending, setSending] = useState(false);
@@ -27,18 +26,17 @@ export function useSendChat(): {
   const appendTaskLog = useAppStore((s) => s.appendTaskLog);
 
   const send = useCallback(
-    async (text: string, mode?: Mode) => {
+    async (text: string) => {
       const trimmed = text.trim();
       if (!trimmed || sending) return;
       setSending(true);
       if (!isWsOpen()) connectWs();
 
-      const m = mode ?? "chat";
-      addUserMessage(trimmed, m);
-      beginAssistant(m);
+      addUserMessage(trimmed);
+      beginAssistant();
 
       try {
-        await chatStream(sessionId, trimmed, m);
+        await chatStream(sessionId, trimmed);
       } catch (err: unknown) {
         // Backend loop not wired or gateway unreachable: show the failure inline
         // rather than leaving a permanently-streaming bubble.
diff --git a/frontend/web/src/modes/ChatShell.tsx b/frontend/web/src/modes/ChatShell.tsx
index 6b24e7b..97b1608 100644
--- a/frontend/web/src/modes/ChatShell.tsx
+++ b/frontend/web/src/modes/ChatShell.tsx
@@ -1,6 +1,5 @@
 import { useEffect, useRef } from "react";
 import { useAppStore } from "../store/useAppStore";
-import { useModeStore } from "../store/useModeStore";
 import { useSendChat } from "../lib/useChat";
 import { MessageBubble } from "../components/chat";
 import { ChatInput } from "../components/ChatInput";
@@ -9,15 +8,14 @@ import { Icon } from "../components/Icon";
 
 /**
  * The single shared page (design/07 §1). All behavior modes live in ONE message
- * stream; each message carries its own `mode`, so its bubble renders per that
- * mode — a session can mix chat / code / home / docs / work / vision shapes.
- * The "input mode" chip above the composer sets the mode of the NEXT message.
+ * stream; each message carries its own `mode` (assigned by the agent at runtime,
+ * design/01 §3 hot-switch), so its bubble renders per that mode. There is no
+ * manual mode selector — the agent / backend drives the mode.
  */
 export function ChatShell(): React.ReactNode {
   const messages = useAppStore((s) => s.messages);
   const { send, sending } = useSendChat();
   const bottomRef = useRef<HTMLDivElement>(null);
-  const setMode = useModeStore((s) => s.setMode);
 
   useEffect(() => {
     bottomRef.current?.scrollIntoView({ behavior: "smooth", block: "end" });
@@ -39,7 +37,7 @@ export function ChatShell(): React.ReactNode {
           <div ref={bottomRef} />
         </div>
       </div>
-      <ChatInput onSend={(t, mode) => void send(t, mode)} sending={sending} onVoice={() => setMode("voice")} />
+      <ChatInput onSend={(t) => void send(t)} sending={sending} onVoice={() => { /* voice handled by agent */ }} />
     </div>
   );
 }